CS8904 datasheet(18/34 Pages) CIRRUS

18 / 34 page

DS191PP2

CS8904

Crystal LAN™ Quad Ethernet Transceiver

CIRRUS LOGIC ADVANCED PRODUCT DATABOOK

4.3.2.2 Changes to Duplex and Auto-Negotiation

Selections

The duplex and Auto-Negotiation selection may be

changed, even after an Auto-Negotiation sequence

has established a good link between a port on the

CS8904 and a remote Ethernet device. The CS8904

allows the system designer to dynamically alter

these selections at any time. The CS8904 will

immediately reconfigure the port to the specified

duplex

and

Auto-Negotiation

operation,

re-

negotiating with the remote Ethernet device if

appropriate. Table 4 summarizes the operation of

Auto-Negotiation as a result of various transitions

of the DUPSEL or AUTSEL pins.

4.3.2.3 Link Status Information

The LINKLED pin provides an LED output to

indicate

that

link

has

been

successfully

established with the remote Ethernet device. This

may occur as a result of normal 10BASE-T

operation or as a result of a successful Auto-

Negotiation. This LED output is capable of sinking

10 mA to drive an LED directly through a series

resistor. The output voltage of each pin is less than

0.4 V when the pin is low. Figure 6 shows a typical

LED circuit.

The LINKLED pin can be used by the controller to

determine if a port has established a valid link with

the remote 10BASE-T device. This pin will be

driven low when a valid link has been established.

Detailed information regarding the duplex selected

and whether the selection was a result of Auto-

Negotiation is available from the DUPLEX and

AUTONEG pins, as described earlier in this

section. If the capabilities selected by the controller

for a port are not compatible with a remote Ethernet

device, then a valid link will not be established and

the LINKLED will be held high.

4.3.2.4 Port Loopback

The CS8904 allows each individual port to be

placed in a loopback mode. Note that this feature is

different from MAU loopback, which is the

loopback

that

occurs

during

the

normal

transmission of data when operating half duplex.

The Port Loopback feature provides a mechanism

to perform network fault isolation and problem

analysis in an Ethernet system device. Port

Loopback may also be used as a means to disable

(partition) a port from the external network. Setting

the LOOP pin high enables this feature.

DUPSEL

AUTOSEL

DUPLEX

AUTONEG

Result Indicated

Low

Forced Half Duplex Operation

High

Low

High

Low

Forced Full Duplex Operation

Low

High

Low

High

Successful Auto-Negotiation; Half Duplex Operation Selected

High

Successful Auto-Negotiation; Full Duplex Operation Selected

High

Low

High

Successful Auto-Negotiation; Half Duplex Operation Selected

High

Low

Unsuccessful Auto-Negotiation; Link Not Operational Selected

Table 3. Auto-Negotiation and Duplex Selection

DUPLEX

AUTOSEL

Re-Negotiation

Transition

Low

Transition

High

Yes

Low to High

Yes

High to Low

Table 4. Auto-Negotiation Operation

LINKSTAT

+5 V

Figure 6. LED Connection Diagram

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